Shares in JJB Sports ended sharply lower on Thursday after reports of disappointing recent sales.
Shares closed down 16.7% after the retailer said same-store sales rose 13.1% between 27 September and 7 November.
However, it said this was "lower than anticipated" given a recent sales promotion, and it reflected the "weakening market environment".
JJB said trading conditions "are having and will continue to have a negative impact" on its full-year forecasts.
It added that the outcome was heavily dependent on the Christmas and New Year trading periods.
Profit margins in the most recent six weeks of trading fell to 33.8%. The latest figures compare to sales growth of 13.4% and an average margin of 40.6% for the year to date.